The present invention relates generally to image output devices and more specifically to reducing engine and halftoning artifacts.
Image output systems such as printer, copiers, facsimile machines receive an input and generate an image based on the received input. Often the input has several shades or various degrees of toning, and the image output device tries to imitate the shade or tone while using inks or other media which are much darker than the desired shade by printing on a sheet of paper that is much lighter than the desired shade. One method for obtaining the desired shade is halftoning. Halftoning is the reproduction of grayscale images using dots of a single shade, but varying their size to simulate the different sizes of grey. Laser printers that cannot print different sized dots produce halftones by varying the number of dots in a given area. Halftoning is also used to produce a black and white version of a color document using shades of gray in place of the original colors.
Simple halftoning methods that are well known in the art can have problems with artifacts, which are manifested as undesirable macro effects. For example, a monochrome default halftoning pattern for a 16×16 cell that has 8 sub-cells can provide the illusion of continuous tone from paper white to device black. If all of the 8 sub-cells grow the same so the code-values for all sub-cells are identical macro effect of equal dot growth can produce horizontal, vertical, slanted line artifacts or repeated pattern artifacts. Halftoning methods which use patterns, often in conjunction with code-values may still exhibit macro effects because of the continuous repetition of the same pattern.
Thus, a need exists for a halftoning method that eliminates line patterns or any other artifact patterns or other macro effects.